Radio/microwave frequency transceiving systems typically rely on superheterodyne architectures to couple high frequency signals from an antenna to a baseband processor. Such architectures typically have standard design features which may include antennas, amplifiers, mixers, oscillators and filters. With the ever-decreasing size of modern communications platforms, space for the circuitry footprints for these components is at a premium. However, previous methodologies for reducing the complexity of superheterodyne transceiving systems have achieved less than optimal results.
Direct conversion transceivers commonly suffer from energy leak from their local oscillators through the mixer to the antenna, thereby resulting in DC offset errors. Additionally, after a period of time, direct conversion transceivers may become unstable due to frequency drift of the local oscillator.
In superheterodyne systems, all signal frequencies are typically converted to a constant intermediate frequency (IF). As such, filters are heavily relied upon to channelize bands of operation and reject interference. Filters typically comprise a large portion of the overall volume of a device. Also, current filters are not amenable to monolithic fabrication and require costly touch labor as they are manufactured from multiple distinct components. Surface acoustic wave (SAW) filters are inherently narrow-band, lossy, have poor group delay response, and are not amenable to monolithic integration. Varactor-based filters typically have high losses, modest intermodulation performance, limited tuning ranges and complex biasing requirements.
Efficient radios architectures also rely on highly linear, low loss switches to select between channels. However, many common switching mechanisms may have high insertion losses, and isolation and linearity characteristics which are less than optimal. Field effect transistor (FET) based semiconductor switches are lossy, exhibit poor isolation, and are prone to intermodulation.
As a result, the demand for ever more flexible, sophisticated, lightweight and low-power transceiver/sensor systems has resulted in the emergence of micro-electromechanical systems (MEMS) technologies. MEMS are the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. While the electronics are fabricated using integrated circuit process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. A brief summary of current MEMS technology and future MEMS development potential may be found in “MEMS for RF/Microwave Wireless Applications: The Next Wave” by Randy J. Richards and Hector J. De Los Santos, Microwave Journal, March 2001 & July 2001, herein incorporated by reference.
MEMS technologies are reaching a point of maturity where filter resonators and switches can be fabricated monolithically and in high density while retaining performance characteristics approaching traditional filter technologies.
Therefore, it would be desirable to provide a MEMS-based broadband transceiver and sensor system.